(1) Field of the Invention
The present invention relates to a linear compressor for reciprocating a piston fitted in a cylinder by a linear motor to draw in, compress and discharge gas.
(2) Description of the Prior Art
In a refrigeration cycle, HCFC refrigerants such as R22 are stable compounds and decompose the ozone layer. In recent years, HFC refrigerants have begun to be utilized as alternative refrigerants to HCFCs, but these HFC refrigerants have the nature for facilitating global warming. Therefore, a study has been started to employ HC refrigerants which do not decompose the ozone layer or largely affect global warming. However, since HC refrigerant is flammable, it is necessary to prevent explosion or ignition so as to ensure safety. For this purpose, it is required to reduce the amount of HC refrigerant to be used to small a quantity as possible. When a general refrigerant is used in the refrigeration cycle, although oil is used as a lubricant, the refrigerant itself also has lubricity. On the other hand, the HC refrigerant itself does not have lubricity and is easily melted into a lubricant.
For these reasons, when the HC refrigerant is used, an oilless or oil pure compressor is required. A linear compressor in which a load applied in a direction perpendicular to an axis of its piston is small and a sliding surface pressure is small is known as a compressor which can be easily realize oilless compression as compared with a reciprocal type compressor, a rotary compressor and a scroll compressor. In the case of the linear compressor the sliding degree of the sliding surfaces between the cylinder and the piston affects the efficiency and durability of the linear compressor. Therefore, considerable complicated means is required for constituting an oilless linear compressor.
In view of the above circumstances, it is an object of the present invention to provide a high-efficiency and reliable linear compressor in which even when a pressing force is applied to its piston, the piston is turnably connected and supported through a connecting rod so that sliding surface pressure between the piston and a cylinder is not increased.
It is another object of the invention to provide a linear compressor capable of enhancing a bearing effect by forming a fluid bearing between its cylinder and piston.
According to a first aspect of the present invention, there is provided a linear compressor comprising a cylinder supported in a hermetic vessel by a support mechanism, a piston slidably supported by the cylinder along its axial direction, a spring member for applying an axial force to the piston, a connecting mechanism for connecting the piston and the spring member with each other, and a linear motor having a stator coupled to the cylinder and a moving member coupled to the piston, wherein the connecting mechanism is connected to the piston such that the connecting mechanism can rock with respect to the piston.
With the first aspect, even if a force trying to incline the piston, e.g., a pressing force caused by a pressing force from a spring member or a magnetic attraction force generated in the linear motor is applied to the piston when the piston is operated, the outer peripheral surface of the piston follows an inner peripheral surface of the cylinder, the sliding surface pressure is reduced, a mechanical loss is reduced, and the efficiency and reliability of the linear compressor are enhanced.
According to a second aspect of the invention, in the linear compressor of the first aspect, the connecting mechanism comprises a connecting rod having one end connected to the piston and the other end connected to the spring member, the one end of the connecting rod is formed into a spherical end, the piston is provided at its axially center portion with a ball seat for holding the spherical end.
With the second aspect, the force applied to the piston is moderated, and the efficiency and reliability of the linear compressor are enhanced.
According to a third aspect of the invention, in the linear compressor of the second aspect, the ball seat is formed in the vicinity of a center of gravity of the piston.
With the third aspect, rotation moment is not applied to the piston, the sliding surface pressure is reduced, and the efficiency and reliability of the linear compressor are enhanced.
According to a fourth aspect of the invention, there is provided a linear compressor comprising a cylinder supported in a hermetic vessel by a support mechanism, a piston slidably supported by the cylinder along its axial direction, a spring member for applying an axial force to the piston, and a linear motor having a coupling portion coupled to the cylinder and a moving member coupled to the piston, wherein a fluid bearing is formed between the piston and the cylinder.
With the fourth aspect, pressure acting on the sliding surface is reduced, the mechanical loss is largely reduced, and the efficiency and reliability of the linear compressor are enhanced.
According to a fifth aspect of the invention, in the linear compressor of the fourth aspect, the fluid bearing comprises a dynamic pressure groove formed in an outer peripheral surface of the piston.
With the fifth aspect, the piston can be held by the dynamic pressure generated in the dynamic pressure groove. As a result, the sliding surface pressure can be reduced, and the efficiency and reliability of the linear compressor are enhanced.
According to a sixth aspect of the invention, in the linear compressor of the fourth aspect, the fluid bearing comprises an introducing path for introducing a discharged gas into the cylinder, and a through hole formed in the cylinder, and the through hole brings the introducing path and a sliding surface of the cylinder.
With the sixth aspect, the pressure between the cylinder and the sliding surface of the piston is largely reduced and as a result, the efficiency and reliability of the linear compressor are enhanced.